1. Field
The present invention relates to a piezoelectric substrate and a surface acoustic wave (SAW) filter, and more particularly, to a piezoelectric substrate and a SAW filter that can improve thermal transmission and remove bi-directional loss by surface wave reflection by a plurality of grooves.
2. Background
A surface acoustic wave (SAW) filter is used as a frequency filter that can generate and distribute elastic surface waves by a voltage when the voltage is supplied and thereby can filter the elastic surface waves. The SAW filter includes various types such as a plurality of normal state interdigital transducer (IDT) electrodes and weighted IDT electrodes. In the case of the normal state IDT electrodes, the overlap size between the electrodes is constant. On the other hand, in the case of the weighted IDT electrodes, the pitch and the overlap size between the electrodes changes.
FIG. 1 is a perspective view of a conventional SAW filter. As shown in FIG. 1, the conventional SAW filter includes a piezoelectric substrate 1, a plurality of IDT electrodes 2 and 3, and a plurality of reflectors 4 and 5. Hereinafter, each component will be described.
The piezoelectric substrate 1 used for the SAW filter is formed by manufacturing lithium niobium oxide (LiNbO3), lithium tantalum oxide (LiTaO3), quartz, and the like in ingot and then subsequently cutting the ingot using a crystal growth scheme. In the case of the piezoelectric substrate applied with the crystal growth scheme, the piezoelectric substrate may have an excellent electrical characteristic. However, when manufacturing such piezoelectric substrate, expensive equipments may be needed and thus manufacturing costs may increase. In order to solve the above problems, the piezoelectric substrate 1 shown in FIG. 1 is applied.
The piezoelectric substrate 1 consists of a wafer 1a made of silicon (Si) or diamond, a piezoelectric member 1b, and a buffer member 1c. 
The plurality of IDT electrodes 2 and 3, and the plurality of reflectors 4 and 5 are formed on the piezoelectric member 1b. The piezoelectric member 1b is formed on the wafer 1a made of Si or diamond. The piezoelectric member 1b may use alumina (Al2O3), AnO, AlN, barium titan oxide (BaTiO3), or PZT series of piezoelectric ceramic and a piezoelectric material with greater piezoelectric coefficient. When disposing the piezoelectric member 1b on the wafer 1a made of Si or diamond, the piezoelectric performance may be deteriorated due to a surface phenomenon. Also, when forming the piezoelectric member 1b on the wafer 1a made of Si, the piezoelectric member 1b is formed in a crystal direction and thus a process condition becomes difficult. In order to solve the above problem, the buffer member 1c is interposed between the wafer 1a and the piezoelectric member 1b. The buffer member 1c uses any one of silicon oxide (SiO2), alumina (Al2O3), and oxide tantalum (Ta2O5) to thereby remove the surface phenomenon when forming the piezoelectric member 1b on the wafer 1a and improve the deterioration of the piezoelectric performance or the process condition.
The plurality of IDT electrodes 2 and 3 includes the input IDT electrode 2 and the output IDT electrode 3 to which input/output electrodes T1 and T2 are connected respectively. A pattern of the plurality of IDT electrodes 2 and 3 is formed by photo etching after forming a conductive material on the piezoelectric substrate 1.
The plurality of reflectors 4 and 5 is formed on the piezoelectric substrate 1 so that the surface elastic wave energy generated from the plurality of IDT electrodes 2 and 3 may be located at an outside of the plurality of IDT electrodes 2 and 3 according to a resonant condition. Through this, it is possible to minimize the surface wave reflection and thereby remove the bidirectional loss. As shown in FIG. 1, the plurality of reflectors 4 and 5 forms a metal film in grating. In addition to the reflectors 4 and 5, an absorber (not shown) is provided to form grooves (not shown) on the piezoelectric substrate 1. When a piezoelectric substrate of a conventional surface acoustic wave (SAW) filter forms a buffer member between a wafer made of silicon (Si) or diamond and a piezoelectric member to thereby improve a surface phenomenon, a serious problem may occur in the crystal structure. Specifically, in comparison to a single crystal, since a thin film is formed, durability power may be decreased. Also, since an absorber including a groove or a reflector in grating structure of a metal thin film on a piezoelectric substrate is formed, it is difficult to reduce the size of the SAW filter.
The present invention is conceived to solve the above described problems and thus provides a piezoelectric substrate that can form an oxide layer with a plurality of grooves on a base member, selectively form a buffer member and a piezoelectric member on the oxide member and thereby can improve thermal transmission by the plurality of grooves and also can be readily manufactured, and a manufacturing method of the same.
The present invention also provides a SAW filter that can form an oxide layer with a plurality of grooves on a base member, selectively form a buffer member and a piezoelectric member on the oxide layer, and thereby can remove bidirectional loss by the surface wave reflection of the plurality of grooves formed on a piezoelectric substrate and thus can reduce the size, and a manufacturing method of the same.
According to an aspect of the present invention, there is provided a piezoelectric substrate including: a base member including an oxide layer with a plurality of grooves on one surface of the base member; a buffer member being formed on the oxide layer to expose one end and another end of the oxide layer; an insulating member being formed on another surface of the base member; and a piezoelectric member being formed on the buffer member.
According to another aspect of the present invention, there is provided a method of manufacturing a piezoelectric substrate, including: forming an oxide layer with a plurality of grooves on one surface of a base member by anodizing; selectively applying a buffer material on the oxide layer to expose one end and another end of the oxide layer to form a buffer member; applying an insulating material on another surface of the base member to form an insulating member; and applying a piezoelectric material on the buffer member to form a piezoelectric member.
According to still another aspect of the present invention, there is provided a surface acoustic wave (SAW) filter including: a base member including an oxide layer with a plurality of grooves on one surface; a buffer member being formed on the oxide layer to expose one end and another end of the oxide layer; an insulating member being formed on another surface of the base member; a piezoelectric member being formed on the buffer member; and a plurality of interdigital transducer (IDT) electrodes being formed on the piezoelectric member to receive an electrical signal, filter the electrical signal, and output the filtered electrical signal.
According to yet another aspect of the present invention, there is provided a method of manufacturing a SAW filter, including: forming an oxide layer with a plurality of grooves on one surface of a base member by anodizing; selectively applying a buffer material on the oxide layer to expose one end and another end of the oxide layer to form a buffer member; applying an insulating material on another surface of the base member to form an insulating member; applying a piezoelectric material on the buffer member to form a piezoelectric member; and applying a conductive material on the piezoelectric member to form a plurality of IDT electrodes by photo etching.